This invention relates to television pincushion correction circuits and in particular to pulse-duration modulation pulse generators useful therein.
A pincushion correction circuit is described in U.S. patent application Ser. No. 722,600, now U.S. Pat. No. 4,088,931, for Peter Edward Haferl and entitled "PINCUSHION CORRECTION CIRCUIT" in which an impedance network is coupled in series with the horizontal deflection coil. The impedance network is paralleled by a controllable switch which is gated into conduction during the horizontal retrace interval. At the top and at the bottom of the vertical scan, corresponding to the beginning and to the end of the vertical scanning interval, the switch is gated on near the last portions of the horizontal retrace interval, thus placing a large average impedance in series with the horizontal deflection winding and reducing the scanning current. Near the center of the vertical scan, the controllable switch is gated into conduction near the center of the horizontal retrace interval, so that the average impedance in series with the horizontal deflection winding is small and the resulting scanning current is comparatively higher.
Gating of the controllable switch in the aforementioned application is controlled by a gating pulse generator synchronized with the horizontal and vertical deflection generators. It is desirable to form the gating pulse generators in a manner suited to integrated circuit (IC) application. In particular, large-value capacitors and extra interface terminals should be avoided. However, suitable circuit controls must be provided.